Progressive climate change is believed to be contributing to reduced rainfall and drought conditions in many regions around the world. Diminishing supplies of water in storage reservoirs and lowering of groundwater tables have lead to the imposition by local government authorities of water restrictions of varying severity upon domestic, commercial and agricultural water users.
While owners of swimming pools can contribute somewhat to water conservation by the use of swimming pool covers to reduce evaporative losses, one major water consuming feature of a swimming pool is the requirement to backwash the pool filtration system to clear the filter of contaminants removed from the pool water, or to lower the water level after a rainstorm.
In a typical domestic swimming pool installation having a volumetric capacity of from 50,000 liters to 70,000 liters, a backwash and rinse cycle for a sand filter will consume between 1000 liters to 10,000 liters each week depending upon the amount of contamination extracted from the pool water by the filter. During the backwash and rinse cycles, water is drawn from the pool via the filter pump and then through the filter medium to a stormwater drain as required by local government authorities. Similarly, when excess water due to rainfall accumulates in the swimming pool, the level is adjusted by pumping many thousands of liters of excess water to the storm water drain or sewer line.
There are potential disadvantages arising from the currently permitted methods of disposal of waste swimming pool water, either into a storm water drain or to a sewer line.
Generally speaking, for swimming pools employing an electrolytic chlorine generator, water in the pool is required to contain about 6000 ppm of sodium chloride (NaCl) for effective operation of the electrolytic chlorinator. Such a high salt content in the backwash and rinse water renders it unsuitable for collection and use for garden irrigation as in other grey water conservation systems due to the gradual accumulation of sodium chloride in the soil leading to degenerative salination of the soil. Ultimately this could give rise to a situation where authorities deem the pool owner's property as a contaminated site requiring expensive rehabilitation.
A prior invention, as described in, for example, PCT/AU2007/000893, addresses this problem by providing an improved method of treating bodies of water using magnesium ions produced in an electrolytic halogenation cell in the water system, optionally including potassium ions, whereby the body of water can be used for, for example, watering a garden as opposed to disposal down a drain or sewer line. These swimming pools are hereinafter referred to as “improved swimming pools”.
In addition to the usual electrolytic chlorinator ordinarily found in a swimming pool system, many government bodies require a swimming pool system to have a backup system for liquid chlorine dosing. Conventional liquid chlorine for use in conventional swimming pools is generated from sodium chloride solutions and added on demand to a swimming pool in need of chlorination, super-chlorination or shock treatment.
Use of conventional liquid chlorine in improved swimming pool water of the sort described above would adversely alter the mineral content in that water and prevent that water from being available for use after backwashing or emptying of the pool.
It would therefore be advantageous to provide a backup mineral dosing system which would not negate the beneficial effects of an improved swimming pool water system, or at least provide the consumer with a choice.
As used herein, the expression “swimming pool” is also intended to embrace the analogous use of spa baths, hot tubs and the like which are operated in a substantially identical manner to swimming pools. Similarly, the expression “backwash” is intended to include all water flows from a swimming pool filter to a storm water drain including backwash, rinse and bypass flows.